1. Field of the Invention
The invention relates to an endoscope telescope having an objective lens-system of adjustable focal length and an optical image-transmitting system which follows on from the objective lens-system and which terminates at a proximal ocular or eye piece lens. Hereinafter such an endoscope telescope will be referred to as an endoscope telescope of the kind described.
2. Description of the Prior Art
In the case of an endoscopic viewing tube it is known from German patent specification No. 1,234,920 to associate a rod-like fibre image-conductor, in a tubular envelope, with an adjustable objective which can be adjusted longitudinally in relation to the image-conductor so that in this way, if the distance between the objective and the object viewed alters, as a result of movement of the image-conductor the image can be re-focussed onto the distal terminal face of the image-conductor, which allows an adjustment to be made for sharpness when the distance to the object viewed changes. On the other hand, for the doctor performing the examination it is of advantage if it is possible for him to alter the scale to which the distance from the object to the objective remains the same. In this way the doctor can always work with the objective sufficiently far away from the object, so that there is no possibility of damage being done in the body cavity. An endoscope telescope for this purpose has already been disclosed in German Auslegeschrift No. 1,766,695 in which the objective consists of two collecting lenses or two groups of lenses which can be moved in unison towards or away from one or another from the proximal end by means of wires or the like, so that on the one hand the scale of reproduction can be altered and on the other hand the image always remains trained on the distal end of the fibre image-conductor. This joint control of the two objective collecting lenses calls for a complicated mechanical arrangement in the telescope tube and for the passage of control wires, with the increase in the diameter of the telescope which this makes necessary. In the case of the adjustable endoscope disclosed in German Pat. No. 1,566,112 the exit pupil alters with enlargement, meaning that the exit pupil is reduced to approximately the same degree as enlargement increases, so that there is then insufficient light available for the taking of photographs or films.
Therefore, it is an object of the invention, where there is a facility for altering the scale of reproduction while the distance to the object viewed remains the same, to compensate, in a simple fashion and while maintaining the image brightness or exit pupil approximately constant, for the movement of the point of focus and thus of the position of the image which occurs when the focal length of the object is altered.